1. Field of the Invention
The present invention relates to an electron beam writing method for writing a fine pattern (uneven pattern) on a resist provided on a substrate by irradiating an electron beam on the resist when manufacturing a discrete track medium, and a fine pattern writing system for implementing the electron beam writing method.
The invention also relates to a manufacturing method of an uneven pattern carrying substrate that includes an imprint mold having an uneven pattern surface formed through a writing step using the electron beam writing method described above.
2. Description of the Related Art
Fine patterns, such as servo patterns and the like, are formed on magnetic disk media. As one of the methods of forming such fine patterns, an electron beam writing method in which patter writing is performed by irradiating an electron beam on a substrate applied with a resist according to the shape of a pattern while rotating the substrate is proposed as described, for example, in U.S. Pat. No. 7,026,098 and Japanese Unexamined Patent Publication No. 2006-184924.
The electron beam writing method described in U.S. Pat. No. 7,026,098 is a method in which when writing, for example, a rectangular or parallelogram element, which constitute a servo pattern, extending in a track width direction, the electron beam is deflected in a radius direction while vibrating rapidly in circumferential directions to scan the beam so as to completely fill the area of the element.
The electron beam writing method described in Japanese Unexamined Patent Publication No. 2006-184924 is a method in which, when writing an element of a record bit string having the same length in a track width direction and different lengths in a track direction, the writing is performed by rapidly vibrating an electron beam in a radius direction of a substrate while controlling the amplitude thereof as the substrate is rotated.
Further, as on/off writing method, a method in which pattern writing is performed by on/off irradiating an electron beam on a substrate applied with a resist according to the shape of a pattern while rotating the substrate, and shifting the substrate or electron beam irradiation unit by one beam width every rotation of the substrate in a radius direction is also known.
Recently, in view of the demand of higher recording density, a discrete track medium (DTM), in which magnetic interference between adjacent data tracks is reduced by separating the tracks with a groove pattern (guard band), has been attracting wide attention.
When writing a fine pattern on such a discrete track medium, the aforementioned electron beam writing methods pose a problem that the methods require a long time to write the fine pattern on the entire surface of the substrate because of a narrower track width and an increased number of tracks to be written due to the formation of groove patterns.
For example, according to the writing method described in U.S. Pat. No. 7,026,098, it is difficult to effectively improve the writing time for the increased number of tracks, although the writing time may be reduced for servo patterns by the employment of the back and forth vibration scheme in comparison with the on/off writing method. In particular, the method has difficulties in accurately writing a groove pattern with a predetermined width, in addition to the problem of having difficulties in reducing the writing time.
That is, according to the writing method described in U.S. Pat. No. 7,026,098, a servo pattern may be written on a discrete track medium with the predetermined characteristics described therein, but when writing a groove pattern on the medium following the servo pattern, if the electron beam is fixedly irradiated to write the groove pattern in an arc shape by the rotation of the substrate, the radiation dose of the electron beam becomes excessive for the groove pattern and the line width is increased by exposure bleeding, thereby posing a problem that a groove pattern having a predetermined width relative to the track width is not written. This is due to the fact that, for the writing of a servo pattern, electron beam intensity is set great to allow scan writing of a predetermined area with a predetermined exposure amount by rapidly vibrating the electron beam in a track direction while the substrate is rotated at a constant speed. It is difficult to reduce the beam intensity when transferring the writing from a servo pattern to a groove pattern from the viewpoint of operational stability of the electron beam radiation unit.
It is possible to secure the writing characteristics for a groove pattern by writing the groove pattern with a different rotation speed and different conditions from those for writing a servo pattern. But this writing method has a problem that the writing time is further extended since a fine pattern for one track is written with a plurality of different rotation speeds of the substrate.
In the mean time, in the writing method described in Japanese Unexamined Patent Publication No. 2006-184924, a groove pattern is written in a manner similar to that described in U.S. Pat. No. 7,026,098, thus the radiation dose becomes excessive in the same way. Therefore, the method also has the problem of having difficulties in writing a groove pattern with a desired width, in addition to the problem of extended time for writing a fine pattern for a discrete track medium on the entire surface of the substrate.
The on/off writing method described above is a suitable method for writing a groove pattern, but it requires a long time for writing servo patterns on the entire substrate, as well as having a problem that it is difficult to write a pattern having a predetermined shape by securing on/off positional accuracy of the electron beam during one rotation of the substrate and positional accuracy in inner and outer circumferences.
Further, if it is possible to write a portion of a fine pattern corresponding to a plurality of tracks during one rotation of the substrate, the time for writing the fine pattern on the entire surface of the substrate will be reduced. But it is difficult to write a portion of a fine pattern of discrete track medium corresponding to a plurality of tracks during one rotation of the substrate, since portions of servo patterns and groove patterns are present in a mixed manner in a single track.
In view of the circumstances described above, it is an object of the present invention to provide an electron beam writing method capable of writing portions of servo patterns and groove patterns in a fine pattern of a discrete track medium corresponding to a plurality of tracks during one rotation of the substrate with a uniform radiation dose, and a fine pattern writing system for implementing the electron beam writing method.
It is a further object of the present invention to provide a manufacturing method of an uneven pattern carrying substrate having a fine pattern accurately written by an electron beam, such as an imprint mold or the like.